Magnetically Induced Anisotropies in the Arrival Directions of Ultra-high-energy Cosmic Rays from Nearby Radio Galaxies

Abstract

Detailed simulations of the arrival directions of ultra-high-energy cosmic rays are performed under the assumption of strong and structured extragalactic magnetic field (EGMF) models. Particles leaving Centaurus A, Virgo A, and Fornax A are propagated to Earth, and the simulated anisotropic signal is compared to the dipole and hotspots published by the Pierre Auger and Telescope Array Collaborations. The dominance of the EGMF structure in the arrival directions of events generated in local sources is shown. The absence of events from the Virgo A direction is related to the strong deviation caused by the EGMF. Evidence that these three sources contribute to an excess of events in the direction of the three detected hotspots is presented. Under the EGMF considered here, M82 is shown to have no contribution to the hotspot measured by the Telescope Array Observatory.

Explaining the UHECR spectrum, composition and large-scale anisotropies with radio galaxies

“…Apart from Centaurus A, also Fornax A (NGC 1316) and Virgo A (NGC 4486) stand out in terms of their extraordinarily high radio flux in the local (< 21 Mpc) Universe. Adding these sources yields also some benefit in explaining the observed arrival directions [26,28]. In addition, several studies have demonstrated that the UHECR spectrum and composition are consistent with UHECRs originating in radio galaxies [29][30][31].…”

Nearby active galactic nuclei and starburst galaxies as sources of the measured UHECRs anisotropy signal

“…In addition to the large-scale anisotropy, the Pierre Auger and the Telescope Array Observatories detected regions in the sky with a relative excess of events. The Pierre Auger Collaboration reported two hotspots regions (HS1 and HS2) for events with energy above 60 EeV [32] centered approximately at (305 • , 25 • ) and (290 • , −70 • ) [33] in galactic coordinates. The Telescope Array Collaboration reported one hotspot (HS3) for events with energy above 57 EeV centered at (146 • .7, 43 • .2) in equatorial coordinates [34].…”

Extragalactic Magnetic Fields and the Arrival Direction of Ultra-high-energy Cosmic Rays

“…The size of the magnetic horizon varies significantly with the direction (Hackstein et al 2016). The flux at Earth from sources located in the interior of galactic clusters, for instance, Virgo A, is highly suppressed by the EGMF (Tanco 1998;de Oliveira & de Souza 2022). The angular power spectrum of the UHECR arrival direction is EGMFdependent.…”